In recent years, organic materials have been replacing conventional inorganic materials in various situations in the field of electronics. Among the organic materials, in particular, a polymer material has advantages of ease of handling, safety, etc., over a low molecular material. Moreover, industry expects much from the polymer material since physical properties of the polymer material can be controlled relatively easily at a low cost using a technique such as copolymerization, polymer blending, or the like.
When the polymer material is used in the field of electronics, an amorphous property, a carrier transport property, etc., are required as important physical properties of the material. If the polymer material can stably have such physical properties, the polymer material can be a satisfactory material in the field of electronics, which can stand comparison with the conventional inorganic material in terms of performance thereof, while making the most use of its advantage. In order to develop the polymer material having such considerable possibilities in the field of electronics, a variety of research and development have been conducted in every aspect of the field.
As an example, in recent years, research and development of a next generation luminescent-type display, which replaces a cathode-ray tube (CRT) and a liquid crystal display (CRT), have been eagerly conducted. Moreover, research and development of a luminescent material and a transport material, which are used in a display element of the next generation luminescent-type display, have been also eagerly conducted.
Examples of the next generation luminescent-type display include a plasma display panel (PDP), a field emission display (FED), an organic electroluminescent display (organic ELD), etc. Among these displays research and development of a luminescent material and a transport material for the organic ELD are conducted with respect to various materials including a polymer material or a low molecular weight material. Moreover, research and development of display elements using these materials also have been eagerly conducted and some of such display elements have been coming into practical use.
A prior art document related to production of an organic ELD display element discloses a process for forming organic thin film layers, such as a luminescent layer, an electron transport layer, a hole transport layer, etc., (for example, see Non-Patent Document 1: “Applied Physics Letters”, Sep. 21, 1987, Vol. 51, No. 12, p. 913). According to the formation process disclosed in Non-Patent Document 1, a low molecular weight material is used as a raw material to form a film using a vacuum deposition method. Moreover, in Non-Patent Document 1, in order to color the thin film formed of the low molecular weight material, luminescent materials having different luminescent colors are deposited at corresponding pixel portions on the low molecular weight thin film via a mask having a prescribed pattern.
On the other hand, another prior art document discloses a process for forming an organic thin film layer using a polymer material (for example, see Non-Patent Document 2: “Applied Physics Letters”, Jul. 7, 1997, Vol. 71, No. 1, p. 34). According to the formation process disclosed in Non-Patent Document 2, a polymer solution is applied on a substrate, and then a solvent in removed from the polymer solution so as to form an organic thin film. Representative examples of a method for applying a polymer solution to a substrate include a spincoating method and an inkjet method.
Further, prior art documents disclose, as a display element of an organic ELD, means for coloring an organic EL element in which a polymer material in used (for example, see Patent Document 1: Japanese Laid-Open Patent Publication No. 7-235376, Patent Document 2: Japanese Laid-Open Patent Publication No. 10-12377, Patent Document 3: Japanese Laid-Open Patent Publication No. 10-153967, Patent Document 4: Japanese Laid-Open Patent Publication No. 11-40358, Patent Document 5: Japanese Laid-Open Patent Publication No. 11-54270, and Patent Document 6: Japanese Laid-Open Patent Publication No. 2000-323276). In these patent documents, an inkjet method, which enables patterning, is used for forming an organic thin film layer.
In the production of an organic thin film element, properties required for thin films included in the organic thin film element include stable luminescent brightness and efficiency, a long-term luminescent life, satisfactory transparency, uniformity, and luminescent stability, etc. In order to obtain theme properties, it is necessary to uniformly disperse or dissolve a luminescent material and a transport material in an amorphous thin film.
Conventionally, the low molecular weight material, which has been mainly used as a raw material of an organic thin film element, is in an amorphous state immediately after the formation of a thin film, and thus the organic thin film element has satisfactory transparency, uniformity and luminescent stability in an early stage of its use. However, such properties cannot last for a long period of time, and therefore the low molecular weight material has practical problems.
Further, in order to produce a thin film for use in an organic thin film element using a low molecular weight material, as conducted in the above-described Non-Patent Document 1, it in necessary to use a vacuum deposition method. However, there is a problem in that it is difficult to produce a large-sized display using the vacuum deposition method.
On the other hand, when the polymer material is used as a raw material of an organic thin film element, the polymer material can be easily brought into a stable amorphous state, and therefore there in an advantage that long-term and stable luminescence can be achieved as compared to the case where the low molecular weight material is used. Moreover, an a method for forming an organic thin film, a relatively easy method in which a polymer solution including a polymer material dissolved in a solvent is applied on a substrate can be employed. Such a method has an advantage of being easily applied to the production of a large-sized display. However, when the polymer material is used as a raw material of the organic thin film element, there is a considerable problem to be solved in that it is difficult to produce a high-quality thin film, that is, a thin film having a uniform thickness and no defects.
Further, an another example of using an organic material in the field of electronics, there in a design for producing an electronic device and conductor lines using the organic polymer material. An one of such cases, in recent years, an organic transistor element including an electrode material, an insulating layer, and a semiconductor layer, which are all produced using the organic polymer material, has been realized an the advance of an inkjet method (for example, see Non-Patent Document 3: Shimoda and Kawase, “Applied Physics”, 2001, Vol. 70, No. 12). In such an organic transistor element, particularly, an organic electrode material including an organic polymer material in required to have a carrier transport property (an electroconductive property and a hole transport property). The degree of the carrier transport property depends on an orientational property of the material, and it is known that as the orientational property of a material increased, the carrier transport property of the material in also increased. In a conventional organic transistor element, PEDOT-PSS, which is generally obtained by adding a polystyrene sulfonate (PSS) to polyethylene dioxythiophene (PEDOT) as a dopant, is used as an organic electrode material. However, PEDOT has a poor orientational property in an electrode and cannot express a sufficient carrier transport property as an electrode material.
Furthermore, in order to increase carrier mobility in an organic semiconductor layer of the organic transistor element, attempts to increase an orientational property of the organic semiconductor layer have been conducted. Specifically, a polymer material such an polyimide or the like is used as a material for an insulating layer, a rubbing treatment is performed on the insulating layer, and an organic semiconductor layer is formed further thereon, so am to increase the orientational property of the organic semiconductor layer. The rubbing treatment can increase the orientational property of the organic semiconductor layer to some degree but the increase in the orientational property is still not recognized an being at a sufficient level. Therefore, the problem that the carrier transport property of the organic electrode material is insufficient is still left unsolved.
As described above, various attempts to apply the organic material to the field of electronics have been conventionally conducted but problems as described below still have been left unsolved up to now.
It is essential for the organic material for use in the field of electronics to have physical properties, ouch as a carrier transport property, an amorphous property, etc., an described above. However, an organic material, which can stably maintain such physical properties and can be easily handled, has not been available yet. When the conventional organic material is used for producing an electronics product, it is not possible to prevent the performance of the electronics product from being deteriorated.
To explain it more specifically, for example, the low molecular weight material, which is mainly used in the conventional organic thin film element and a method for producing such an element, cannot achieve long-term and stable luminescence. The reason for this is that when an organic thin film is formed using a low molecular weight material, the low molecular weight material is gradually crystallized over a lapse of time, thereby causing the physical properties, such as transparency and the like, of that thin film to be nonuniform. Moreover, when a polymer material is used for a luminescent layer and a transport layer of the organic thin film element, long-term and stable luminescence can be achieved as compared to the case where a low molecular weight material is used. However, it in very difficult to form a thin film having a uniform thickness and no defects using a conventional production method. The reason for this is that in the case of the polymer material, the viscosity of a solution of that material becomes larger as the molecular weight of the material becomes greater, which makes it difficult to apply the solution on a substrate using a spincoating method, an inkjet method, or the like.
The present invention is provided in view of the above-described problems and an objective thereof is to provide a polymer material having a carrier transport property which allows the formation of a thin film on the scale of several tons of nanometers, which has a superior amorphous property while having a uniform thickness and no defeats and can be used for an organic EL element and the like. Another objective of the present invention is to provide a method for producing an organic thin film element using such a polymer material.
When an organic polymer material on which a heat treatment, a rubbing treatment, etc., are performed is applied to an electronic device and conductor lines, the oriental property of the material can be improved, thereby, increasing a carrier transport property, which is one of the properties essential to the use as the electronic product and conductor lines, to some degree. However, merely performing a rubbing treatment or the like does not necessarily provide the polymer material with a sufficient orientational property. As a result, the polymer material in not provided with a sufficient carrier transport property. Moreover, it is difficult for the conventional organic polymer material to maintain its orientational property for a long period of time, and therefore there in a disadvantage that a life of an electronics product using the organic polymer material is short.
The present invention is also provided in view of such problems, and objectives of the present invention are to provide an electronic device and conductor lines which use an organic polymer material having a considerable orientational property, and thus having a considerable carrier transport property, and capable of maintaining its performance for a long period of time.